Added missing onclone option accordingly with official documentation

types/html2canvas/index.d.ts

@@ -1,6 +1,6 @@
 // Type definitions for html2canvas.js 1.0-alpha
 // Project: https://github.com/niklasvh/html2canvas
-// Definitions by: Richard Hepburn <https://github.com/rwhepburn>, Pei-Tang Huang <https://github.com/tan9>, Sebastian Schocke <https://github.com/sschocke>
+// Definitions by: Richard Hepburn <https://github.com/rwhepburn>, Pei-Tang Huang <https://github.com/tan9>, Sebastian Schocke <https://github.com/sschocke>, Rickard Staaf <https://github.com/Ristaaf>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.3
 
@@ -35,6 +35,9 @@ declare namespace Html2Canvas {
         /** Whether to log events in the console. */
         logging?: boolean;
 
+        /** Callback function which is called when the Document has been cloned for rendering, can be used to modify the contents that will be rendered without affecting the original source document. */
+        onclone?: { (doc: HTMLDocument): void };
+
         /** Url to the proxy which is to be used for loading cross-origin images. If left empty, cross-origin images won't be loaded. */
         proxy?: string;